This invention relates to cleaning debris from orifices in an ink jet printhead nozzle plate.
Many different types of digitally controlled printing systems of ink jet printing apparatus are presently being used. These ink jet printers use a variety of actuation mechanisms, a variety of marking materials, and a variety of recording media. For home applications, digital ink jet printing apparatus is the printing system of choice because low hardware cost makes the printer widely affordable. Another application for digital ink jet printing uses large format printers. These large format printers are expected to provide low cost copies with an ever improving quality. Ink jet printing technology is the first choice in today""s art. Thus, there is a need for improved ways to make digitally controlled graphic arts media, such as billboards, large displays, and home photos, for example, so that quality color images may be made at a high-speed and low cost, using standard or special paper.
Ink jet printing has become recognized as a prominent contender in the digitally controlled, electronic printing arena because of its non impact, low-noise characteristics, its use of papers from plain paper to specialized high gloss papers and its avoidance of toner transfers and fixing. Ink jet printing mechanisms can be categorized as either continuous ink jet or droplet on demand ink jet.
Continuous ink jet printing generally involves using electric charge to selectively direct a stream of ink droplets. On demand type ink jet printers selectively produce individual ink droplets at each of many ink jet orifices. A typical consumer type printer includes approximately 30 to 200 orifices on the nozzle plate. At every orifice, a pressurization actuator is used to produce the ink jet droplet. Typical on demand ink jet printers use one of two types of actuators to produce the ink jet droplet. The two types of actuators are heat and piezo materials. With a heat actuator, a heater at a convenient location heats ink and a quantity of the ink will phase change into a gaseous steam bubble and raise the internal ink pressure sufficiently for an ink droplet to be expelled to a suitable receiver. The piezo ink actuator incorporates a piezo material. Material is said to possess piezo electric properties if an electric charge is produced when a mechanical stress is applied. This is commonly referred to as the xe2x80x9cgenerator effect.xe2x80x9d The converse also holds true, in that an applied electric field will produce a mechanical stress in the material. This is commonly referred to as the xe2x80x9cmotor effect.xe2x80x9d
Inks for high speed jet droplet printers have a number of special characteristics. Typically, water-based inks have been used because of their conductivity and viscosity range. For use in a jet droplet printer, preferred inks are electrically conductive, having a resistivity below about 5000 ohm-cm and preferably below about 500 ohm-cm. For good flow through small orifices, water-based inks generally have a viscosity in the range between about 1 to 15 centipoise at 25 degree C. Preferred inks additionally are stable over a long period of time, compatible with the materials comprising the nozzle plate and ink manifold, free of living organisms, and functional after printing. Preferred after printing characteristics are smear resistance after printing, fast drying on paper, and waterproof when dry. An ideal ink also incorporates a nondrying characteristic in the jet cavity so that the drying of ink in the cavity is hindered or slowed to such a degree that through occasional spitting of ink droplets the cavities can be kept open. The addition of glycol will facilitate the free flow of ink through the ink jet. Also it is of benefit if ink additives prevent the ink from sticking to the ink jet printhead surfaces.
Ink jet printing apparatus typically includes an ink jet printhead that is exposed to the various environment where ink jet printing is utilized. The orifices are exposed to all kinds of air borne particles. Particulate debris accumulates on the printhead surfaces, forming around the orifices. The ink may combine with such particulate debris to form an interference burr to block the orifice or cause through an altered surface wetting to inhibit a proper formation of the ink droplet. That particulate debris has to be cleaned from the orifice to restore proper droplet formation. This cleaning commonly is achieved by wiping, spraying, vacuum suction, and/or spitting of ink through the orifice. The wiping is the most common application.
The present invention provides improved cleaning of the nozzle plate of an ink jet printhead. The invention provides an ink jet printing apparatus wherein the cleaning liquid can be effectively used to provide for improved cleaning with a minimum number of parts and operations. The present invention provides for non-contacting cleaning of particulate debris, thereby eliminating the need of traditional wiper blades or other mechanical contact methods. This invention also permits use and disposal of a defined quantity of cleaning fluid for each printhead and each cleaning cycle, providing fresh cleaning fluid for each cleaning operation, and eliminating the need for multiple cleaning stations.
A pair of rollers have substantially parallel axes of rotation. The outer surfaces of the rollers contact one another along a substantially horizontal contact line, forming above the contact line a roller cavity. A dispenser dispenses a predetermined amount of cleaning fluid into the roller cavity. A drive mechanism connected to at least one of the rollers rotates the roller about its axis of rotation. The rollers are operatively connected so that as one rotates in one direction, the other rotates in the opposite direction. The drive mechanism is capable of rotating one of the rollers in a first direction, so that the second roller rotates in the opposite direction, to tend to retain the cleaning fluid in the roller cavity, and agitate the cleaning fluid. The printhead orifice plate can then be brought into contact with the agitated cleaning fluid (but not the rollers themselves). After the cleaning fluid has cleaned the orifice plate, the drive mechanism reverses the rotation of the rollers to remove the cleaning fluid from the roller cavity.